US jets will not be sent to intercept Edward Snowden, the wanted intelligence whistleblower, if he flies out of Russia to seek a safe passage to another country, Barack Obama has said.

"I'm not going to be scrambling jets to get a 29-year-old hacker," said the US president during a visit to Senegal.

His comment came as mystery persisted over Mr Snowden's whereabouts after he failed to show up for a third time for a flight to Havana, Cuba, at Moscow's Sheremetyevo Airport.

Vladimir Putin, the Russian president, said on Tuesday that the former CIA and National Security Agency contractor was in the airport's transit zone after flying in from Hong Kong on Sunday. He was expected to fly on to Cuba on a flight path that can skirt US airspace.

Mr Snowden, who turned 30 last week, is wanted on espionage charges in the US after disclosing details of alleged surveillance of Americans' telephone calls and emails.

He is seeking a safe haven and has reportedly applied for asylum in Ecuador. Reporters have combed Sheremetyevo's departures and transit zone all week looking for the American without seeing him, leading to speculation that Russian officials have helped him stay in a closed area, where they may be questioning him.

A Russian immigration source said that passengers could stay in the transit zone "as long as they want" but would not be able to enter Russia proper without a visa.

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"There has been no request from the foreign ministry or President Putin to issue a visa (to Mr Snowden), and he has not asked for one," he added.

There was no sign of Mr Snowden as an Aeroflot plane left Sheremetyevo's Gate 25 for Havana yesterday.

Mr Obama said he had not spoken to Mr Putin or China's president, Xi Jinping, about Mr Snowden.